As class AB amplifiers have good audio performance, they are widely used in audio devices. But the power consumption of class AB amplifiers is so large that they may not be used in portable devices which are powered by batteries.
Class D amplifiers are another type amplifier which have good audio performance and consume less power. In operation, class D amplifiers convert an analog signal to a digital signal (e.g. pulses) and then convert the digital signal back into an amplified analog signal. In the process of the signal conversion, many kinds of disturbances may affect the output signal of class D amplifiers, and this may make it uncomfortable for the listener.
In operating time of class D amplifiers, audible pop noises are always presented by transient events. If a big sound signal starts/finishes suddenly or audio devices having the class D amplifiers stop/start suddenly, pop noises generated in these events are easily to be heard by the listener.
Because of steps of fabrication process, both offset of input stages of the class D amplifiers and mismatching of resistors in feedback loop may contribute to offset in output. Without any suppression, this offset (especially when this offset is bigger than 20 mV) is easy to cause audible pop noise at the transient events that the output stage starts to switch on or switch off. If a large audio signal starts from a silent environment or a large audio signal stops suddenly, the listener may feel uncomfortable. This event is also one kind of pop noise.